This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-247123, filed Sep. 1, 1999, No. 11-247124, filed Sep. 1, 1999 and No. 11-251172, filed Sep. 6, 1999; the entire contents of which are incorporated herein by reference.
The present invention relates in general to a thin-film solar cell module and a method of manufacturing the same. In particular, this invention relates to an electrode lead-out structure and a method of fabricating the same in a thin-film solar cell module comprising a single thin-film solar cell or a combination of thin-film solar cells. The thin-film solar cell comprises a plurality of photovoltaic (PV) elements formed on a transparent insulating substrate.
Attention has been paid to sunlight power generation as means for overcoming environmental problems such as an exhaustion of natural resources or an increase in generation of carbon dioxide. Thin-film solar cells have attracted particular attention because the amount of semiconductor material to be used, such as silicon, is small.
Solar cells using crystalline silicon substrates have conventionally been put into practice. Compared to the solar cells, thin-film solar cells have a problem in that the efficiency of converting light to power is inferior by several-ten percentage. In an environment in which foot print for placing solar cells is limited, as in Japan, it is very important to increase as much as possible that portion of the area occupied by solar cell modules, which contributes to power generation, thereby reducing the gap in conversion efficiency between the solar cells and the thin-film solar cells.
As regards the solar cell using a crystalline silicon substrate, one solar cell is formed on one crystalline silicon substrate. Several-ten solar cells are connected to constitute a solar cell module. Since it is necessary to provide gaps for disposing a solar cell module and areas for disposing wiring for sending power of solar cell elements to connection means such as a terminal box, the area of a power generation section for converting light to power is set at about 70% to 80% of the entire area of the solar cell module. In the field of thin-film solar cell modules, a structure has been proposed wherein solar cell elements are formed directly on a transparent insulating substrate and the solar cell elements are connected on the substrate (hereinafter referred to as xe2x80x9csubstrate-integration-type solar cell modulexe2x80x9d). In the substrate-integration-type solar cell module, the area of the power generation section can be increased to more than 90% of the entire area occupied by the module.
U.S. Pat. No. 4,292,092 discloses a structure of a solar cell portion in the substrate-integration-type solar cell module, and a method of fabricating the same. According to the technique of U.S. Pat. No. 4,292,092, a transparent conductor film is provided on a transparent insulating substrate of, e.g. glass. The transparent electrode film is divided by a laser process into strip-shaped photovoltaic (PV) regions. P-type, i-type and n-type amorphous silicon is provided on the entire surfaces of the PV regions, and thus PV semiconductor layers are formed. Connection grooves for connecting adjacent solar cell elements are formed by a laser process in parallel to and away from a first line formed by a laser process. After a back electrode layer is formed, separation grooves are formed in the back electrode layer in parallel to the connection grooves and opposite to the separation grooves of the transparent conductor film. Through these processes, a thin-film solar cell is fabricated wherein a plurality of strip-shaped photovoltaic (PV) elements are connected in series on a single substrate.
Buses for outputting power from the thin-film solar cell is provided on the transparent insulating substrate. Since the buses are portions not contributing to power generation, they are formed of a material with good electrical conductivity to efficiently deliver generated power and are disposed on strip-shaped bus regions which are slightly narrower than the PV elements. Examples of the method of forming the buses are disclosed in Jpn. Pat. Appln. KOKAI Publication No. 3-171675 wherein a paste in which metallic particles of glass frit, etc. are dispersed is coated on bus regions, or in Jpn. Pat. Appln. KOKAI Publication No. 9-83001 wherein a solder-plated copper foil is disposed on bus regions by means of a solder for ceramics.
The solar cell module using the crystalline silicon substrate and the thin-film solar cell module have each a connection means (hereinafter referred to merely as xe2x80x9cthe connection meansxe2x80x9d) for outputting power. A terminal box can be used for the connection means. The terminal box includes terminals, and wiring elements lead out of the solar cell module are connected via the terminals to an output power cable.
According to some examples of the connection structure between the bus and the connection means for the substrate-integration-type solar cell module, copper foils are arranged and connected on such a transparent support member as used in the crystalline silicon substrate solar cell in the same two-dimensional fashion as the crystalline silicon substrate, or a paste in which metallic particles of glass frit, etc. are dispersed is linearly coated on peripheral portions of the transparent insulating substrate where no PV elements are provided, as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 3-171675.
There is such a problem with these methods that due to a large space needed for wiring an area for power generation in the limited area of the solar cell module is occupied.
To overcome this problem, Jpn. Pat. Appln. KOKAI Publication No. 9-326497 proposes a technique wherein wiring (solder-plated copper foils, etc.) for connecting the buses and the connection means is disposed in a filler for sealing photovoltaic (PV) elements. This document describes a prior-art method for maintaining electrical insulation between the wiring (copper foils) and PV elements, wherein an insulating film is used and a filler and a back cover are disposed on the insulating film. This document also describes an embodiment wherein copper foils are coated with insulating films.
The former method will now be described with reference to FIG. 2. Buses (solder-plated copper foils) 4, 4xe2x80x2 are provided on bus regions 3, 3xe2x80x2 on a thin-film solar cell 100. Wiring elements 5, 5xe2x80x2 for connecting the buses and the aforementioned connection means are disposed between the solder-plated copper foils 4, 4xe2x80x2. An insulating film 7 is provided under the wiring elements 5, 5xe2x80x2. The wiring elements 5, 5xe2x80x2 (two solder-plated copper foils) are connected at one end to the solder-plated copper foils 4, 4xe2x80x2. A filler film 9 and a back protection cover 13 are provided over the wiring elements. Openings 14 for taking out electrodes are formed in the back protection cover 13. In the state in which the solder-plated copper foils 5, 5xe2x80x2 are led out of the back cover via the openings, the back protection cover 13 is thermally pressed with the filler film 9 interposed by means of a vacuum laminator and fixed on a glass substrate 1.
The latter method described in Jpn. Pat. Appln. KOKAI Publication No. 9-326497 will now be described with reference to FIG. 3. In FIG. 3, the wiring elements 5, 5xe2x80x2 are replaced with copper foils 45, 45xe2x80x2 formed by coating the two solder-plated copper foils 5, 5xe2x80x2 with insulating films 15. In this method, the insulating film 7 used in the example of FIG. 2 is not used.
According to a resent research work, it is recognized that the method of Jpn. Pat. Appln. KOKAI Publication No. 3-171675 has a problem in that the characteristics of the solar cell module deteriorate due to a large area required for wiring.
It is also recognized by a modern research that the method shown in FIG. 2 permits easy assembly but no filler can be put under the solder-plated copper foils 5, 5xe2x80x2. Because of this problem, if the solder-plated copper foils 5, 5xe2x80x2 are pulled from the openings 14, gaps are created between the solder-plated copper foils 5, 5xe2x80x2 and insulating film 7.
According to a modern research, in the structure shown in FIG. 3, too, gaps are similarly created between the coated copper foils 45, 45xe2x80x2 and the PV elements.
These thin-film solar cell modules were tested by an environmental test device at a humidity of 85% and a temperature of 85xc2x0 C. After 1,000 hours, these thin-film solar cell modules were observed, and it turned out that water entered the above-mentioned gaps and back electrodes near the gaps corroded. Where the insulating films 15 were coated on the copper foils using an adhesive other than the filler, the color of the filler 9 near the insulating films 15 was changed to yellow.
The solar cell module is disposed on the roof, etc. of a house, and the temperature thereof rises up to about 80xc2x0 C. The solar cell module is susceptible to such environmental effects. The life of about 20 years is required for solar cell modules for reasons of market needs. Thus, there are very strict requirements for reliability of solar cell modules. To meet the requirements, it is necessary to use materials whose reliability has been certified, to completely fill the inside of the solar cell modules with filler, and to eliminate any gap from the inside.
It has been recognized that there is such a problem that an edge portion of the opening 14 in the back protection cover comes in contact with the wiring element (solder-plated copper foil) 5, 5xe2x80x2 with a very high possibility in the module fabricated by the method as shown in FIG. 2. Specifically, in this module, there is no means for restricting the positional relationship between the wiring and the opening. As a result, this module has such a structure that the wiring and the opening may come in contact with high possibility. Where a sheet including metallic material, such as a three-layer sheet of Tedler/Al/Tedler, is used for the back protection cover, a short-circuit may occur in the wiring elements 5, 5xe2x80x2 due to the metallic material in the sheet. In another case where an aluminum frame is used as a frame, power may leak to the frame via metallic material in the back protection cover. Neither a means for protecting the filler at the opening nor a means for preventing water from entering via the opening is provided at the opening in the protection cover of the module having the structure shown in FIG. 2. This considerably decreases the reliability of the module.
In fact, it turned out that as regards the thin-film solar cell modules having the above structure, about 30% of products were defective. When accepted products were tested by an environmental test device for 1,000 hours at a humidity of 85% at a temperature of 85xc2x0 C., entrance of water was observed at the opening.
In order to put sunlight power generation to wide and common use, it is necessary to reduce the price of sunlight power generation systems while meeting the above-described strict requirements for reliability. For this purpose, it is also necessary to improve the structure of solar cells and the method of manufacturing the same, thereby meeting the above requirements.
The means for overcoming the above problems have been improved and developed, with the structure disclosed in Jpn. Pat. Appln. KOKAI Publication No. 9-326497 employed as a starting point, and simple and clear means as recited in the claims have been achieved.
According to a first aspect of the present invention, there is provided a thin-film solar cell module characterized by comprising:
a transparent insulating substrate;
a thin-film solar cell formed on the transparent insulating substrate;
a bus connected to the thin-film solar cell and formed on the transparent insulating substrate;
sealing means provided on a surface of the thin-film solar cell;
connection means for outputting power from the thin-film solar cell; and
a wiring element for connecting the bus and the connection means,
wherein the thin-film solar cell has on the transparent insulating substrate a plurality of photovoltaic elements each comprising a transparent electrode layer, a photovoltaic thin-film semiconductor layer and a back electrode layer,
the sealing means comprises a filler and a back protection cover,
the wiring element is buried in a filler, and
an insulating sheet buried in a filler is disposed between the wiring element and the back electrode layer.
According to a second aspect of the invention, in the thin-film solar cell module according to the first aspect, the insulating sheet is one of a glass nonwoven fabric sheet and a 160xc2x0 C.-heat-resistant synthetic fiber fabric sheet.
According to a third aspect of the invention, there is provided a thin-film solar cell module characterized by comprising:
a transparent insulating substrate;
a thin-film solar cell formed on the transparent insulating substrate;
a bus connected to the thin-film solar cell and formed on the transparent insulating substrate;
sealing means provided on a surface of the thin-film solar cell;
connection means for outputting power from the thin-film solar cell; and
a wiring element for connecting the bus and the connection means,
wherein the thin-film solar cell has on the transparent insulating substrate a plurality of photovoltaic elements each comprising a transparent electrode layer, a photovoltaic thin-film semiconductor layer and a back electrode layer,
the sealing means comprises a filler and a back protection cover, the back protection cover having a metallic film therein and having an opening in which the wiring element is passed, and
the sealing means further comprises at least one insulator covering the opening of the back protection cover.
According to a fourth aspect of the invention, there is provided a method of manufacturing a thin-film solar cell module, characterized by comprising the steps of:
forming a thin-film solar cell, the step of forming the thin-film solar cell including,
forming a photovoltaic layer by successively stacking, on a transparent insulating substrate, a transparent electrode layer, a photovoltaic thin-film semiconductor layer and a back electrode layer,
dividing the photovoltaic layer into a plurality of regions and forming a plurality of photovoltaic elements, and
forming on the transparent insulating substrate a bus for deriving power from the photovoltaic elements;
forming a wiring element between the bus and connection means for deriving power from the thin-film solar cell; and
forming sealing means including a filler and a back protection cover,
wherein the step of forming the wiring element includes,
disposing successively a filler, an insulating sheet and a filler on the thin-film solar cell and under the wiring element, and
the step of forming the sealing means includes,
disposing, on an entire surface of the thin-film solar cell, a filler sheet having an opening for leading out the wiring element to the connection means, and
disposing, on the filler sheet, a back protection cover having a hole at a position corresponding to the opening of the filler sheet.
According to a fifth aspect of the invention, in the method of manufacturing a thin-film solar cell module according to the fourth aspect, the insulating sheet disposed under the wiring element is one of a glass nonwoven fabric sheet and a 160xc2x0 C.-heat-resistant synthetic fiber fabric sheet.
According to a sixth aspect of the invention, there is provided a method of manufacturing a thin-film solar cell module, characterized by comprising the steps of:
forming a thin-film solar cell, the step of forming the thin-film solar cell including,
forming a photovoltaic layer by successively stacking, on a transparent insulating substrate, a transparent electrode layer, a photovoltaic thin-film semiconductor layer and a back electrode layer,
dividing the photovoltaic layer into a plurality of regions and forming a plurality of photovoltaic elements, and
forming on the transparent insulating substrate a bus for deriving power from the photovoltaic elements;
forming a wiring element between the bus and connection means for deriving power from the thin-film solar cell; and
forming sealing means including a filler and a back protection cover,
wherein the step of forming the sealing means includes disposing an insulating sheet having an opening for passing the wiring element between the back protection cover and the filler sheet.
In the thin-film solar cell modules and the methods of manufacturing the thin-film solar cell modules according to the first to sixth aspects of the invention, it is preferable that the filler in which the wiring element is buried and the filler in which the insulating sheet is buried be formed of the same material as the filler of the sealing means.
It is also preferable that the insulating sheet have the same color tone as the back protection cover.
It is also preferable that the insulating sheet be formed of the same resin material as the back protection cover, and have the same color tone as the back protection cover.
It is also preferable that the wiring element be one of a copper wire and a copper foil which are coated with one of solder and tin.
It is also preferable that the filler in which the wiring element is buried and the filler in which the insulating sheet is buried be formed of a material having the same color tone as the back protection cover.
It is also preferable that the two fillers and the filler sheet disposed under the wiring element be formed of a material which is melted by heat and cross-linked.
It is also preferable that the filler in which the wiring element is buried and the filler in which the insulating sheet is buried be formed of one selected from the group consisting of ethylene-vinyl acetate copolymer (EVA), silicone, and polyvinylbutyral (PVB).
It is also preferable that at least one of the wiring element and the bus be a solder-plated copper foil having a width of 2 mm or more, and a thickness of solder of the solder-plated copper foil be 50 xcexcm or more.
It is also preferable that at least one of the wiring element and the bus be a solder-plated copper foil having a width of 2 mm or more, and a thickness of solder of the solder-plated copper foil be 100 xcexcm or more and 200 xcexcm or less.
It is also preferable that the insulating sheet have the same color tone as the back protection cover.
It is also preferable that the insulator be an insulator sheet having an opening through which the wiring element is tightly passed, and the insulator sheet be disposed in a space between the back protection cover and the solar cell.
It is also preferable that the insulator be buried in the filler.
It is also preferable that the insulator be one of a fluorine-based resin film, a glass nonwoven fabric and a 160xc2x0 C.-heat-resistant fiber nonwoven fabric.
It is also preferable that the insulator covering the opening of the back protection cover have one of a notch and an opening.
In the methods of manufacturing the thin-film solar cell modules according to the fourth to sixth aspects of the invention, it is also preferable that, following the step of forming the wiring element and the step of forming the sealing means, there be provided a step of fixing, by a vacuum lamination step, the thin-film solar cell, the back protection cover, and the filler, the filler sheet, the wiring element and the insulating sheet provided between the thin-film solar cell and the back protection cover.
It is also preferable that the two fillers and the filler sheet disposed under the wiring element be formed of the same material.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.